How to pick the right channel for your WiFi network

Why my Wi-Fi is slow? Why the signal drops out?

When your deploy a wireless network you can encounter one or more symptoms: reduced range, sudden drops in transfer speeds, the wireless signal dropping out in certain places or at certain times during the day, your wireless signal strength going up and down randomly.

In these kinds of context, it’s very important to be sure that, when deploying new Wi-Fi networks, the impact with previously deployed and existing WLAN is minimized.

What can I do?

The main 2 items to be checked are usually the IP PLAN and the CHANNEL PLAN.

IP Plan

In relation to the first aspect, the most important thing is to avoid IP conflicts. IP conflicts happenwhen 2 or more networking devices have the same IP address (layer-3) and are able to communicate within the same LAN (layer-2), then the sender does not know to whom deliver the specific IP packet due to the conflict: basically it’s like if 2 units claims to be the receiver of the specific packet and there is no way to know who will be picked.

To avoid such situation, it’s very important to know how the LAN is designed, how it is partitioned in collision domains and how many NAT levels are cascaded. The typical situation in an environment where a DSL router is installed is that such router has a WAN port with a public IP, provided dynamically by the ISP, and has an IP class shared among all the LAN ports, such as 192.168.1.1/24, which means that clients connecting to LAN ports will receive an IP address between 192.168.1.2 and 192.168.1.254.

In such cases, it’s better to leave the added AP configured to work in DHCP mode (Dynamic IP), which means that it will receive an IP address in such range, behaving exactly as other clients.

To know the exact assignment of IP addresses to Wi-Fi clients, it will be possible to check the DHCP Lease Table, available in the configuration tool of the DSL router / gateway and similar to the one in the picture below.

If the DSL router has a Wi-Fi interface, then the same criteria has to be applied, as the SSID is usually bridged to the LAN ports and share the same DHCP range.

If there is need to assign a Static IP to the added AP, then it’s important to verify the DHCP range of the DHCP Server embedded in the DSL Router.

This operation is usually done accessing the web interface or configuration tool of the gateway / DSL router.

The static IP assigned to the new AP connected to one of the gateway LAN ports does NOT have to be included in the DHCP RANGE, otherwise an IP conflict is likely to happen between the AP and a network client receiving such IP from the DHCP Server.

Reducing intereference

In relation to the second aspect, i.e. reducing interference, the best practice is to do a quick site survey and verify which channels are already in use.

In order to do such operation, there are a lot of free tools for Windows, Mac, Linux.

Example: in a venue with a Wi-Fi DSL router in place, the site survey might provide the following result:

– SSID A / Hair Saloon / channel 1 / power 4/5

– SSID B / Café Nero / channel 11 / power 3/5

– SSID C / Café Nero / channel 9 / power 5/5

In a situation like this, the best channel to pick is 6, which is not overlapping to the neighbours SSIDs.

If possible, it’s recommended to turn off the Wi-Fi of the DSL of the venue where the AP is being added, in order to remove useless interference. If such SSID has to be active, it has to be considered as a source of interference.

As the interference sources can change over time, it’s recommended to use remote channel management tools in order to change the channel when needed.

The Tanaza Dashboard includes botha tool to easily change the channel, a triggered email alert when there is an increase of interference and, in the future, a channel orchestration mechanism to automatically remove the issue.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 873466.

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